The solid oxide fuel cell (hereinafter, referred to as SOFC) is known as a high efficiency fuel cell with a wide range of uses. The operating temperature of the SOFC is increased to increase the ionic conductivity, so air discharged from the compressor of a gas turbine can be used as air (oxidizing agent) supplied to the air electrode side. Also, high-temperature fuel that could not be used in an SOFC can be used as the fuel in the combustor of a gas turbine.
Therefore, various combinations of SOFC, gas turbine, and steam turbine have been proposed as power generation systems that can achieve high efficiency power generation, as disclosed in, for example, Patent Document 1. The combined system disclosed in Patent Document 1 includes an SOFC, a gas turbine combustor that burns exhaust fuel gas and exhaust air discharged from the SOFC, and a gas turbine having a compressor that compresses air for supply to the SOFC.